Methods that have proved successful in the non-destructive testing of inert materials have been and will continue to be used to quantify the mechanical properties of viable animal tissues and of materials used to replace tissues. The strength of this group of investigators lies in (1) their long experience with the behavior of living tissues, (2) their knowledge of medical needs for information about animal tissues, (3) their familiarity with the physics, mathematics, and computer techniques necessary for thorough use of data derived from experiments, as well as (4) knowledge of the ways that data obtained from experiments can be used in the training of medical personnel responsible for the care of patients. These assets will continue to be directed toward establishing the mechanical properties of tissues obtained from a wide variety of organs: urinary bladder, eyes, esophagus, ureter, uterus, and extraocular muscles. Efforts will continue to keep these tissues, when studied in vitro, in a state as close to viable as possible and to develop physically valid methods for testing these tissues in vivo. The aim is to obtain system parameters for several human organs so that this and other laboratories can continue to develop ways to obtain accurate numerical values for biological variables that must be known for the proper training of physicians and proper care of patients. These include: (1) esophageal motility in health and disease, (2) the rate of healing of cardiac and aortic wounds, (3) muscular molecular events related to muscular mechanical properties, (4) properties of sutures and (5) the effects of sutures on tissues. These data are not being supplied by any other laboratories as yet.